This invention relates to elastomeric microspheres and their uses in delivery and controlled release of agriculturally active agents, particularly insect pheromones.
Pheromones are chemical compounds that influence specific patterns of behavior in a particular type of animal species. The use of pheromones to control insect populations offers several advantages over other methods of insect control. Unlike pesticides, pheromones are species specific; no major disruption or threat to the overall environment occurs. Also, insect populations respond to low levels of pheromones, so the threat of a high concentration of toxins or contaminates can be mitigated. Pheromones can effectively control various insect populations such as the Codling Moth, Grape Berry Moth, Pink Boll Worm, Tomato Pinworm and Spotted Fireworm.
Microencapsulation of agriculturally active agents demonstrates several advantages over other delivery methods. Microencapsulated materials should be safer to handle, reduce the total amount of active material needed, and reduce the potential for leaching while maintaining biological activity. Also, microencapsulated materials enable site-specific delivery of the active material. Site-specific delivery reduces the effective dose while increasing the therapeutic effect of the active material.
There are a number of techniques available in the art for microencapsulating agriculturally active materials. Solvent evaporation, interfacial polymerization, emulsion polymerization or drying techniques represent a few of these methods. Limitations exist for all these methodologies. Solvent evaporation or spray drying techniques typically incorporate organic. solvents. Interfacial polymerization can be inhibited by active materials that contain reactive functionalities. For example, alcohols are difficult to encapsulate by existing interfacial methods because they can react rapidly with electrophilic monomers (see e.g., Hall, D. R., Marrs, G. J. Insect Pheromones in Plant Protection, Jutsum, A. R. and Gordon, R. F. S. eds, John Wiley and Sons, 1989, p. 220). Conventional emulsion polymerization techniques generally fail to adequately incorporate water insoluble materials. The term xe2x80x9cconventional emulsion polymerization techniquesxe2x80x9d refers to heterogeneous polymerization methods utilizing a water-soluble initiator and relying on monomer diffusion.
Several approaches have been described to microencapsulate agriculturally active agents. Typically, polymers with a high glass transition temperature are used. For example, poly(xcex1-methyl stryene), and poly(methyl methacrylate) have been used to affect release of herbicides such as atrazine, metribuzin, alachlor, and metolachlor. However, herbicides combined with poly(xcex1-methyl stryene), and poly(methyl methacrylate) failed to show consistent, high activity.
Thus, a need exists for alternative techniques for encapsulating agriculturally active agents that may be used to prepare releasably encapsulated agriculturally active agents.
Briefly, in one aspect of the present invention, a releasably loaded elastomeric microsphere is provided comprising a releasable agriculturally active agent within the boundary of the elastomeric microsphere. Releasable agriculturally active agents can include for example, pheromones, herbicides, pesticides and the like. These agents may or may not be soluble in polymerized elastomeric microspheres or in their monomeric precursors. Uniquely, the agriculturally active agent can be incorporated into the microsphere using either a post polymerization addition process or an in-situ addition process.
Advantageously, loading microspheres with a releasable agriculturally active agent within the boundaries of the microspheres provides a unique delivery device that can be fashioned to provide characteristics that are application specific. Examples of such delivery devices include but are not limited to substrates (such as tapes, sheets of material and the like) coated with the releasably loaded elastomeric microspheres; sprayable dispersions; or suspensions of these elastomeric microspheres and the like.
Another advantage is that elastomeric microspheres provide a unique way to modify release rates because polymer matrices can be modified to influence release rates. Also, the use of releasably loaded elastomeric microspheres offers the opportunity to create tacky particles capable of adhering to a substrate and provide delivery of agriculturally active agents. Tacky releasably loaded elastomeric microspheres eliminate the need to formulate conventionally encapsulated agriculturally active agents with sticky latex polymers to adhere encapsulated materials to a target substrate. Such tacky releasably loaded elastomeric microspheres can be used to deliver agriculturally active agents to difficult places, such as forest canopies, with sustained lasting power to environmental forces (wind, rain, etc.). The agriculturally active agent that is enclosed within the releasably loaded elastomeric microspheres may be either a liquid or a solid. Solid agriculturally active agents are first suspended in the monomer mixture or a solvent, but may be contained in the microsphere in the solid form due to either polymerization and/or evaporation of the solvent. Liquid agriculturally active agents may be added to the monomer mixture or added directly to the microsphere.
Finally, the releasably loaded elastomeric microspheres of the present invention can be formulated into sprayable mixtures, either as dispersions or suspensions, allowing for easy application and handling.
In another aspect of the present invention, the releasably loaded elastomeric microspheres can be prepared using a post polymerization addition process, wherein polymerized elastomeric microspheres are blended with a releasable agriculturally active agent or mixture of agents under such conditions to cause the releasable agriculturally active agent to be absorbed within the boundaries of the elastomeric microspheres. The process for preparing such releasably loaded elastomeric microspheres comprises the steps of:
(a) providing polymerized elastomeric microsphere precursors;
(b) blending the polymerized elastomeric microsphere precursors with a releasable agriculturally active agent or mixture of agents, wherein the releasable agriculturally active agent or mixture of agents is optionally dissolved in a solvent and such that the releasable agriculturally active agent is absorbed within the boundaries of the polymerized elastomeric microsphere precursors and;
(c) optionally, removing the solvent.
An alternative in-situ addition process for preparing releasably loaded elastomeric microspheres comprises the steps of:
(a) forming an oil phase comprising at least one oil soluble monomer, an oil soluble initiator and a releasable agriculturally active agent or a portion of the releasable agriculturally active agent in a water phase comprising at least one suspension stabilizer or surfactant;
(b) initiating polymerization of the oil phase in the water phase; and
(c) optionally, adding remaining releasable agriculturally active agent.
In this application:
xe2x80x9cboundary or boundariesxe2x80x9d mean the outside limits of the elastomeric microspheres"" polymeric structure;
xe2x80x9celastomericxe2x80x9d means amorphous or noncrystalline materials that can be stretched and that will retract rapidly to substantially their original dimensions upon release of the force;
xe2x80x9cagriculturally activexe2x80x9d means a composition that produces a response in cultivated soil, crops, and/or livestock;
xe2x80x9creleasablexe2x80x9d means when the elastomeric microsphere is placed in its intended environment of use, an agriculturally effective amount of the agriculturally active agent diffuses out of the microsphere;
xe2x80x9creleasably loadedxe2x80x9d means all or a portion of an agriculturally active agent is contained within the optical boundaries of the elastomeric microspheres in an amount sufficient to diffuse out of the microsphere;
xe2x80x9csolventxe2x80x9d means conventional organic liquids generally used in the industry that include, for example, toluene, heptane, ethyl acetate, methyl ethyl ketone, acetone, and mixtures thereof and does not include water;
xe2x80x9cpartially water misciblexe2x80x9d means the solubility of the compound in water is less than 98% but greater than 0.5% by weight, that is, if one gram of the compound is put in 100 grams of water, 0.98 grams would dissolve; and
xe2x80x9cwater immisciblexe2x80x9d means the solubility of the compound in water is less than 0.5% by weight.